US3537001A - Multifrequency tone detector - Google Patents

Multifrequency tone detector Download PDF

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Publication number
US3537001A
US3537001A US781461A US3537001DA US3537001A US 3537001 A US3537001 A US 3537001A US 781461 A US781461 A US 781461A US 3537001D A US3537001D A US 3537001DA US 3537001 A US3537001 A US 3537001A
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Prior art keywords
counter
clock
tone
frequency
output
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US781461A
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English (en)
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Joseph J Friend
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AT&T Corp
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Bell Telephone Laboratories Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q1/00—Details of selecting apparatus or arrangements
    • H04Q1/18—Electrical details
    • H04Q1/30—Signalling arrangements; Manipulation of signalling currents
    • H04Q1/44—Signalling arrangements; Manipulation of signalling currents using alternate current
    • H04Q1/444—Signalling arrangements; Manipulation of signalling currents using alternate current with voice-band signalling frequencies
    • H04Q1/45—Signalling arrangements; Manipulation of signalling currents using alternate current with voice-band signalling frequencies using multi-frequency signalling
    • H04Q1/457—Signalling arrangements; Manipulation of signalling currents using alternate current with voice-band signalling frequencies using multi-frequency signalling with conversion of multifrequency signals into digital signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q3/00—Selecting arrangements
    • H04Q3/42—Circuit arrangements for indirect selecting controlled by common circuits, e.g. register controller, marker

Definitions

  • the counter output states at the instant they are read determine the period of the wave and conseqently the fundamental frequency thereof.
  • Decoder logic connected in a predetermined manner to the counter output, establishes clock count lbands which correspond to the recognition bandwidth limits of the multiplicity of tones to be detected; a distinct output indication is provided if the count in the counter, at the read instant, falls within one of said clock count bands.
  • This invention relates to a multifrequency detector for use in decoding frequency coded decimal digits in a telephone system.
  • LC resonant circuits Two prime requirements of a multifrequency tone detector, for use in the telephone plant, are good selectively and rapid response. That is, the detector must be suiciently selective as to guard against digit simulation (operation in the presence of a signal resembling in some Way a valid tone signal) by speech or other noise introduced at the telephone transmitter; and, to provide an acceptable speed of service, the detector must be quick to respond to a valid tone signal.
  • groups of tuned circuits i.e., LC resonant circuits
  • the typical LC resonant circuit suffers from a decrease in quickness of response With increased selectivity. Accordingly, the design engineer must trade-off speed of response against selectivity. That is, one cant have it both ways. To achieve rapid response some sacrifice in selectivity must lbe made, and vice versa.
  • a related object is to provide a multifrequency tone detector which can be as frequency selective as necessary, while at the same time being quick to respond to a valid signal.
  • Multifrequency tone detectors are generally timeshared, at the central office, between a number of subscriber lines. Nevertheless, the number of detectors needed in the telephone plant is still so great that the cost, size and complexity thereof are of prime consideration. And here again, the prior art LC resonant circuit arrangements are not without their shortcomings. Typically, they are bulky and more costly than one might desire.
  • a digital tone detector is utilized in decoding the frequency coded decimal digits used for signaling in a telephone system. Tone detection is accomplished by timing the intervals between alternate zero crossings of the input tone waveform.
  • Tone detection is accomplished by timing the intervals between alternate zero crossings of the input tone waveform.
  • a multistage binary counter is driven by a reference clock source of relatively high clock frequency. The counter is reset to zero immediately after detection of a given first zero crossing and subsequently read ⁇ upon detection of the third or next alternate zero crossing. The counter output states, at the instant the counter is read, determine the period of the waveform and hence the fundamental frequency of input tone signal.
  • Decoder logic connected in a predetermined manner to the counter output, establishes clock count bands which correspond to the recognition bandwidth limits of the multiplicity of tones to be detected. A distinct output indication of tone is provided if the count in the counter, at the read instant, falls within one of the clock count bands established by the decoder logic.
  • inhibit logic is used to prevent operation in response to signals other than those tones in the frequency bands of interest.
  • the single ligure is a detailed block diagram schematic of a multifrequency tone detector in accordance with the principles of the present invention.
  • the multifrequency tone detector of the present invention is intended for use in a telephone signaling arrangement wherein the digit-calling information is coded in the form of two frequencies in the voice frequency range, each chosen from a distinct group of frequencies, and transmitted simultaneously to the telephone central oflice.
  • the total number of signal frequencies is eight, divided into two groups of four (i.e., a low frequency group and a high frequency group), and a valid signal is made up of one frequency from each group of four.
  • the following table lists eight typical signal frequencies (Hz.) or tones to be detected and the ve percent recognition bandwidth limits for each.
  • the longest period corresponds to the lowest frequency of interest, namely, 680 HZ.
  • a full period, at this frequency, is 1471 microseconds (aseo.)
  • the upper edge of the lowest frequency band is 714 Hz. which has a period of 1400 laseo.
  • the following table lists the periods corresponding to the band edges of the low group.
  • a multistage binary counter driven by a reference clock signal, is used to measure the periods of the input waveforms.
  • the desired band edge resolution will dictate the clock frequency, i.e., the neness of the desired measurement will specify the number of divisible units in the time scale.
  • acceptable band edge resolution is achieved if the time measuring scale is divided into 256 units (28). A full count of 256 will correspond to the longest period to be measured, i.e., 1471 ,usec.
  • clock frequency for the low group is thus dictated to be:
  • the minimum time unit of measure is 5.746 asec.
  • the following table gives the clock counts corresponding to the band edge periods of the immediately preceding table.
  • the band edge clock counts are identical for both groups.
  • the only thing that distinguishes the high group detector from the low group one is the clock frequency used, the circuitry is 4 identical.
  • the clock frequency for the high group is computed to be 301.8, kHz.
  • the tone signals generated at ⁇ a subscriber location are received at a central office -where the two groups are separated by means of band pass filters (not shown).
  • the high and low groups of tones are then respectively delivered to separate digital tone detectors such as shown in the drawing. Under normal operating conditions the signal tones of a given group are presented sequentially to the detector circuit.
  • An incoming tone signal is applied to the limiter 11 where it is squaredup to approximately square-wave form, after 'which zero crossing spikes are produced by the RC dilferentiator circuit 12.
  • Circuitry of the above nature is well known in the art.
  • the positive spikes, or negative spikes-the choice being with the circuit designer, are applied as gate signals to the pulse sync circuit 13; clock pulses derived from a source (not shown) of known periodicity are also coupled to circuit 13.
  • the clock frequency is quite high with respect to the multifrequency tones to be detected.
  • a positive spike gates the pulse sync circuit ON and the first clock pulse immediately thereafter is thus permitted to pass; the clock pulse then functions to reset the pulse sync circuit.
  • the READ pulses from the pulse sync circuit 13 are used to read out the states of the four temporary stores 14-17 into the hold circuits 24-27. These stores and hold circuits may typically be comprised of conventional flip-flops.
  • the read out operation is carried out by delivering the READ pulses as enabling signals to the appropriate AND gates, such as gates 18 and 19. Initially it can be assumed that the temporary stores 14-17 are empty so that all the hold circuits 24-27 are set to the 0 state by said read out operation.
  • the READ pulses from the pulse sync circuit 13 are delayed one clock period in unit delay 21 and then used to CLEAR all stages of the eight stage counter 22 and all the temporary stores 14-17.
  • the stores 14-17 are cleared or set to the 0 state by delivering the CLEAR pulses to the reset terminals R1 of the stores.
  • the unit delay insures that the information in the temporary stores is read out prior to the resetting of the latter.
  • the counter 22 is reset to its zero condition by a CLEAR pulse and thereafter it advances or counts in a typical binary counting fashion in response to the clock pulses coupled to the input thereof.
  • the binary counter 22 comprises eight stages and hence it will county to 255, recycle to 0 and begin once again, if not reset or inhibited.
  • the counter can be of most any conventional configuration.
  • decoders are of AND gate configuration; the input of each decoder is coupled to the output leads of the counter 22 in the ⁇ designated manner.
  • airline connections from the counter output to the various decoders are utilized.
  • Each counter stage has two output leads and each decoder is coupled to one or the other of the output leads of each counter stage.
  • the output leads of the counter stages have been labeled using a conventional notation.
  • the output of the first stage of the counter consists of a one (l) and a not-one lead. If this stage is set to its l state, the (1) output lead is energized, whereas with the stage set to its 0 state, the (I) output lead is energized.
  • the count registered by the counter 22 will always be one clock count less than the total number of clock cycles that occur between alternate zero crossings of the input waveform. This accounts for the apparent count discrepancy (of one clock count) between the band edge clock counts listed in the last of the above tables and the band edge clock counts established by the decoder logic.
  • the counter will be reset to zero and then, once again, begin counting the input clock pulses coupled thereto.
  • the 179 decoder sets the temporary store 14 to its 1 state. If a second pulse subsequently emerges from the pulse sync circuit 13 before the counter reaches the count of 189, the l in the temporary store 14 will be read into the hold circuit 24 Via the enabled AND gate 18.
  • the (l) output lead of hold circuit 24 is thus energized, which indicates that a zero crossing interval of acceptable duration has been received, e.g., a 941 Hz. signal tone has been received, if the detector is connected to receive the low frequency group.
  • the 189 decoder serves to reset the temporary store 14 to its 0 state.
  • the counter then continues to count through the following bands where a similar operation of the decoder logic takes place. In the presence of a valid input tone one, and only one, of the temporary stores will be set to the l state at the read time thereof.
  • the 189, 208, 231 and 255 decoders have their output leads connected directly to the reset terminals of temporary stores 14, 15, 16, and 17, respectively; these output leads are also respectively connected to the reset terminals of hold circuits 24, 25, 26, and 27. Accordingly, as the count in the counter reaches the clock counts of 189, 208, 231, and 255 the associated temporary stores and hold circuits are immediately reset. Any output indication from a hold circuit is thus quickly terminated when the responsible input signal tone ceases.
  • the single input AND gate 29, connected in the output lead of the 255 decoder, is for isolation purposes.
  • the 255 decoder If the counter reaches a count of 255 before the neXt zero crossing occurs, the 255 decoder resets the temporary store 17 and the hold circuit 27, as heretofore described, and in addition it stops counter operation by direct-setting the first two counter stages. In this manner, the counter will be latched-up and will not recycle until it is once again cleared. This procedure prevents a possible false indication with certain frequencies lower than those of interest, e.g., certain subharmonics.
  • the instant tone detector circuit produces a distinct output indication of the input signal immediately after the detection of the first zero crossing interval of accepted duration.
  • This output indication appears as an energizing signal on one, and only one, of the hold circuit leads.
  • the output indication will be continuous as long as the in-band tone is received; and the output indication is terminated no later than approximately one cycle period after the input tone has ceased.
  • the output indications from the several hold circuits are ultimately delivered to a call signal register where they are accumulated and stored until the signaling sequence is complete.
  • the register than functions in conjunction with the other central office equipment to set up the call through the otiice.
  • the recognition bandwidth limits i.e., frequency selectivity
  • Band edge resolution can be chosen at will and the same increases eX- ponentially with the addition of counter stages and an increase in clock frequency.
  • the instant detector in addition, possesses excellent discrimination against signals other than those desired; signals having the proper interval between zero crossings are a small class of waveforms.
  • a multifrequency tone detector comprising a multistage counter, a source of clock pulses of known periodicity, the clock frequency of said source being relatively high with respect to the multifrequency tone signals to be detected, means coupling said clock pulses to said counter to establish a typical counting operation therein, means for setting the counter to an initial condition immediately after the occurrence of a given rst zero crossing of an input waveform, means for reading the output state of the counter upon the occurrence of a given subsequent zero crossing of said input waveform, decoder means connected to the counter output and serving to establish clock count bands which correspond to the recognition bandwidth limits of the plurality of input tones to be detected, and means coupled to said decoder means for providing a distinct output tone indication when the count in the counter at the read time thereof falls within one of said clock count bands.
  • a multifrequency tone detector as defined in claim 1 including means for temporarily inhibiting said counting operation when the count reaches a predetermined number.
  • a multifrequency tone detector as defined in claim 2 wherein a distinct output indication is produced immediately after the detection of the first zero crossing interval of accepted duration.
  • a multifrequency tone detector as defined in claim 4 including means for terminating said output tone indication within substantially one cycle period after said in-band tone signal has ceased.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Telephonic Communication Services (AREA)
  • Use Of Switch Circuits For Exchanges And Methods Of Control Of Multiplex Exchanges (AREA)
  • Measuring Frequencies, Analyzing Spectra (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
US781461A 1968-12-05 1968-12-05 Multifrequency tone detector Expired - Lifetime US3537001A (en)

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US78146168A 1968-12-05 1968-12-05

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US (1) US3537001A (enrdf_load_stackoverflow)
BE (1) BE742628A (enrdf_load_stackoverflow)
DE (1) DE1960407C3 (enrdf_load_stackoverflow)
FR (1) FR2025426A1 (enrdf_load_stackoverflow)
GB (1) GB1221890A (enrdf_load_stackoverflow)
NL (1) NL167074C (enrdf_load_stackoverflow)
SE (1) SE345056B (enrdf_load_stackoverflow)

Cited By (32)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3760269A (en) * 1972-07-31 1973-09-18 Gte Automatic Electric Lab Inc Multi-frequency tone detector
US3784758A (en) * 1969-10-20 1974-01-08 Tel Tone Corp Pulse ratio detector
US3845399A (en) * 1973-08-30 1974-10-29 Sperry Rand Corp Digital detector of an analog signal
US3935395A (en) * 1973-08-16 1976-01-27 International Standard Electric Corporation Selective signal receiver for use in telecommunication systems
US3949177A (en) * 1973-08-16 1976-04-06 International Standard Electric Corporation Method for frequency-recognition in selective signal receivers for use in telecommunication, particularly telephone systems
US3959603A (en) * 1974-10-29 1976-05-25 Tone Technology Corporation Dual tone multiple frequency receiver/decoder
US3962645A (en) * 1974-11-06 1976-06-08 General Electric Company Tone frequency detecting circuit
US3971897A (en) * 1973-08-16 1976-07-27 International Standard Electric Corporation Circuit arrangement for a selective signal receiver, particularly for use in telephone systems
US3979562A (en) * 1974-11-29 1976-09-07 Rice Dale E Decoder
US3993875A (en) * 1975-05-23 1976-11-23 Houston Natural Gas Corporation Tone receiver
US4002988A (en) * 1975-07-29 1977-01-11 Sperry Rand Corporation Programmable high pass digital filter of analog signal
US4002989A (en) * 1975-07-29 1977-01-11 Sperry Rand Corporation Programmable low pass digital filter of analog signal
US4004236A (en) * 1975-07-29 1977-01-18 Sperry Rand Corporation Programmable bandpass digital filter of analog signal
US4009353A (en) * 1975-06-23 1977-02-22 International Business Machines Corporation Analog signal detection
US4016371A (en) * 1976-01-26 1977-04-05 Rockwell International Corporation Frequency tone detection
US4016370A (en) * 1975-03-19 1977-04-05 Chestel, Inc. Digital tone decoder
US4028501A (en) * 1976-03-04 1977-06-07 Northern Electric Company Limited Method and apparatus for translating multiple frequency signalling
US4042787A (en) * 1976-05-17 1977-08-16 Stromberg-Carlson Corporation Output processing and output coupling circuit for a digital tone receiver
US4044206A (en) * 1975-11-25 1977-08-23 Melco Digital decoder for multiple frequency telephone signalling
US4045620A (en) * 1976-05-10 1977-08-30 Conrac Corporation Digital tone detector
US4055730A (en) * 1975-05-29 1977-10-25 Comex Systems, Inc. Circuit for detecting dial pulses
US4061885A (en) * 1975-12-17 1977-12-06 Motorola, Inc. Digital tone decoder
US4090133A (en) * 1977-01-06 1978-05-16 Bell Telephone Laboratories, Incorporated Digital time interval sensor using a free running counter and a cycle counter with only the latter being reset at each event
US4119808A (en) * 1976-06-17 1978-10-10 General Instrument Corporation Multi-frequency receiver circuits
US4187403A (en) * 1977-03-23 1980-02-05 Siemens Aktiengesellschaft Voice-protected, frequency-selective signal receiver
US4386239A (en) * 1980-06-17 1983-05-31 Bell Telephone Laboratories, Incorporated Multifrequency tone detector
US4412299A (en) * 1981-02-02 1983-10-25 Teltone Corporation Phase jitter detector
US4675898A (en) * 1984-12-07 1987-06-23 Buscom Systems, Inc. Single tone telephone receiver
US4692710A (en) * 1985-09-04 1987-09-08 Electronic Design & Research, Inc. Fundamental and harmonic pulse-width discriminator
US4751576A (en) * 1985-09-06 1988-06-14 Deutsch Itt Industries Gmbh Digital circuit for classifying the frequency of a signal in frequency ranges
US5307404A (en) * 1990-06-28 1994-04-26 Sharp Kabushiki Kaisha Signal detecting device
US6735303B1 (en) * 1998-01-08 2004-05-11 Sanyo Electric Co., Ltd. Periodic signal detector

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT330252B (de) * 1972-09-28 1976-06-25 Siemens Ag Sprachgeschutzer frequenzselektiver zeichenempfanger fur fernmelde-, insbesondere fernsprechanlagen
JPS53149076A (en) * 1977-06-01 1978-12-26 Sony Corp Digital frequency detecting circuit

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2992384A (en) * 1959-07-06 1961-07-11 Thompson Ramo Wooldridge Inc Frequency counter
US3039685A (en) * 1957-03-27 1962-06-19 Hewlett Packard Co Electronic counter
US3413449A (en) * 1965-04-26 1968-11-26 Bell Telephone Labor Inc Rate registering circuit

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3039685A (en) * 1957-03-27 1962-06-19 Hewlett Packard Co Electronic counter
US2992384A (en) * 1959-07-06 1961-07-11 Thompson Ramo Wooldridge Inc Frequency counter
US3413449A (en) * 1965-04-26 1968-11-26 Bell Telephone Labor Inc Rate registering circuit

Cited By (33)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3784758A (en) * 1969-10-20 1974-01-08 Tel Tone Corp Pulse ratio detector
US3760269A (en) * 1972-07-31 1973-09-18 Gte Automatic Electric Lab Inc Multi-frequency tone detector
US3935395A (en) * 1973-08-16 1976-01-27 International Standard Electric Corporation Selective signal receiver for use in telecommunication systems
US3949177A (en) * 1973-08-16 1976-04-06 International Standard Electric Corporation Method for frequency-recognition in selective signal receivers for use in telecommunication, particularly telephone systems
US3971897A (en) * 1973-08-16 1976-07-27 International Standard Electric Corporation Circuit arrangement for a selective signal receiver, particularly for use in telephone systems
US3845399A (en) * 1973-08-30 1974-10-29 Sperry Rand Corp Digital detector of an analog signal
USRE28997E (en) * 1973-08-30 1976-10-05 Sperry Rand Corporation Digital detector of an analog signal
US3959603A (en) * 1974-10-29 1976-05-25 Tone Technology Corporation Dual tone multiple frequency receiver/decoder
US3962645A (en) * 1974-11-06 1976-06-08 General Electric Company Tone frequency detecting circuit
US3979562A (en) * 1974-11-29 1976-09-07 Rice Dale E Decoder
US4016370A (en) * 1975-03-19 1977-04-05 Chestel, Inc. Digital tone decoder
US3993875A (en) * 1975-05-23 1976-11-23 Houston Natural Gas Corporation Tone receiver
US4055730A (en) * 1975-05-29 1977-10-25 Comex Systems, Inc. Circuit for detecting dial pulses
US4009353A (en) * 1975-06-23 1977-02-22 International Business Machines Corporation Analog signal detection
US4002989A (en) * 1975-07-29 1977-01-11 Sperry Rand Corporation Programmable low pass digital filter of analog signal
US4002988A (en) * 1975-07-29 1977-01-11 Sperry Rand Corporation Programmable high pass digital filter of analog signal
US4004236A (en) * 1975-07-29 1977-01-18 Sperry Rand Corporation Programmable bandpass digital filter of analog signal
US4044206A (en) * 1975-11-25 1977-08-23 Melco Digital decoder for multiple frequency telephone signalling
US4061885A (en) * 1975-12-17 1977-12-06 Motorola, Inc. Digital tone decoder
US4016371A (en) * 1976-01-26 1977-04-05 Rockwell International Corporation Frequency tone detection
US4028501A (en) * 1976-03-04 1977-06-07 Northern Electric Company Limited Method and apparatus for translating multiple frequency signalling
US4045620A (en) * 1976-05-10 1977-08-30 Conrac Corporation Digital tone detector
US4042787A (en) * 1976-05-17 1977-08-16 Stromberg-Carlson Corporation Output processing and output coupling circuit for a digital tone receiver
US4119808A (en) * 1976-06-17 1978-10-10 General Instrument Corporation Multi-frequency receiver circuits
US4090133A (en) * 1977-01-06 1978-05-16 Bell Telephone Laboratories, Incorporated Digital time interval sensor using a free running counter and a cycle counter with only the latter being reset at each event
US4187403A (en) * 1977-03-23 1980-02-05 Siemens Aktiengesellschaft Voice-protected, frequency-selective signal receiver
US4386239A (en) * 1980-06-17 1983-05-31 Bell Telephone Laboratories, Incorporated Multifrequency tone detector
US4412299A (en) * 1981-02-02 1983-10-25 Teltone Corporation Phase jitter detector
US4675898A (en) * 1984-12-07 1987-06-23 Buscom Systems, Inc. Single tone telephone receiver
US4692710A (en) * 1985-09-04 1987-09-08 Electronic Design & Research, Inc. Fundamental and harmonic pulse-width discriminator
US4751576A (en) * 1985-09-06 1988-06-14 Deutsch Itt Industries Gmbh Digital circuit for classifying the frequency of a signal in frequency ranges
US5307404A (en) * 1990-06-28 1994-04-26 Sharp Kabushiki Kaisha Signal detecting device
US6735303B1 (en) * 1998-01-08 2004-05-11 Sanyo Electric Co., Ltd. Periodic signal detector

Also Published As

Publication number Publication date
DE1960407A1 (de) 1970-07-23
BE742628A (enrdf_load_stackoverflow) 1970-05-14
NL167074C (nl) 1981-10-15
GB1221890A (en) 1971-02-10
SE345056B (enrdf_load_stackoverflow) 1972-05-08
NL6918250A (enrdf_load_stackoverflow) 1970-06-09
FR2025426A1 (enrdf_load_stackoverflow) 1970-09-11
NL167074B (nl) 1981-05-15
DE1960407C3 (de) 1979-04-05
DE1960407B2 (de) 1978-08-17

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